All results lower than expected.

When you saying shifted downward, are you referring to the retention time, or the concentration?  Are these fresh standards and controls?  Did the person performing the PM on the instrument change the column/liner?  Did you verify that they correct column/liner were reinstalled, and done correctly?  Also try reloading the method to the instrument in case a parameter was changed manually.  

I am referring to the concentration. These are commercial controls that are opened fresh and used. I made sure the column was inserted on the inlet side and the detector side. To my knowledge the liner was replaced. 

I will also add the area under my peak seems to have remained somewhat where they should. Pre maintenance the area under my acetone peak ranged from 1059-1100 and now it ranges between 997-1059. So I don't feel I have any loss of resolution. However concentrations are much lower. 

If your area is relatively stable but your amount/result is low, you have to have either altered your calibration values, failed to clear a previous calibration, or omitted a dilution factor.  Are all results lower by the same factor or is it variable?

I calibrated after maintenance was performed, ensuring the calibration  values were entered correctly. I will check once more, but I am certain they are correct. I have attached three images of three of my volatiles, with the values pre maintenance and values post maintenance.

The constant low values are post maintenance 

Hi Linds.

I have the exactly same issue. Did you solved the problem?

Hi Linds.

I have the exactly same issue. Did you solved the problem?